The present invention relates to an image display apparatus for medical, industrial, or domestic purpose and, more particularly, to an image display apparatus which shows the viewer two target images different from each other.
Conventional stereoscopic image display apparatuses are generally classified into two categories. One is an apparatus by which the viewer wears spectacles having a function of dividing an image into right and left images. The viewer can view stereoscopic images for the right eye and the left eye, which are time-divisionally displayed on the image display screen, with the right eye and the left eye alone, respectively. The other is an apparatus in which a lenticular plate is adhered on the image display screen. With the image dividing function of this lenticular plate, the viewer can view stereoscopic images for the right eye and the left eye with the right eye and the left eye alone, respectively.
FIG. 1 shows the arrangement of one example of the conventional stereoscopic image display apparatuses as described above. Reference numeral 60 denotes spectacles having the function of dividing an image into right and left images; 61a and 61b, liquid crystal shutters; 62, a synchronous circuit; and 63, a color CRT as an image display apparatus.
The operation of the stereoscopic image display apparatus according to the first conventional example with the above arrangement will be described below. The color CRT 63 time-divisionally, alternately displays stereoscopic images for the right eye and the left eye. The liquid crystal shutter 61a of the spectacles 60 is opened into a transmitting state only when the right-eye stereoscopic images are displayed. The liquid crystal shutter 61b is opened into a transmitting state only when the left-eye stereoscopic images are displayed. The shutters 61a and 61b are thus controlled by the synchronous circuit 62. This allows a viewer wearing the spectacles 60 to view only the right-eye stereoscopic images with the right eye and only the left-eye stereoscopic images with the left eye. As a result, a stereoscopic vision is obtained.
FIG. 2A shows the arrangement of a stereoscopic image display apparatus according to a second conventional example. Reference numeral 71 denotes a lenticular plate consisting of a number of cylindrical lenses formed into stripes; and 72, a color CRT as an image display apparatus.
The operation of the stereoscopic image display apparatus according to the second conventional example with the above arrangement will be described below. The color CRT 72 displays stereoscopic images for the right eye and the left eye at alternate arbitrary positions arranged into slit-like shapes each having a width nearly one half of the stripe width of the lenticular plate 71. Through the individual cylindrical lenses of the lenticular plate 71, the right eye of the viewer views only the right-eye stereoscopic images displayed in the slit-like shapes, and the left eye of the viewer views only the left-eye stereoscopic images displayed in the slit-like shapes. Consequently, a stereoscopic vision is attained.
Unfortunately, in the stereoscopic image display apparatus of the first conventional example described above, the spectacles having the function of dividing an image into right and left images is essential in order to permit the right and left eyes of the viewer to independently view the stereoscopic images. Wearing these spectacles is troublesome to the viewer. In addition, flicker occurs in the displayed stereoscopic images since it is necessary to time-divisionally switch the right- and left-eye stereoscopic images. This is an obstacle in viewing the stereoscopic images.
On the other hand, in the stereoscopic image display apparatus of the second conventional example the viewer views stereoscopic images through the stripe lenses. Consequently, the allowable range of the position of the viewer at which the stereoscopic vision is possible is narrowed. The result is severe limitations that images degrade when the viewer moves, and it is difficult for a large number of viewers at arbitrary positions to view the stereoscopic images. Also, the apparatus is expensive because image processing for displaying stripe images is required.